The present invention relates to a control equipment power source for supplying power to control equipment, such as numerical control equipment.
In general, control equipment, such as numerical control equipment, contains a memory circuit, an I/O interface circuit and so forth in addition to a control circuit, such as a processor. In the case where the control circuit and the I/O interface circuit and so on operate on different drive voltages, a control equipment power source arrangement is required that provides a power source for supplying electric power necessary for operating the control circuit (which power source will hereinafter be referred to as the control circuit power source) and a power source for supplying electric power necessary for driving the memory circuit for its read/write operations and for driving the I/O interface circuit (which power source will hereinafter be referred to as the driving power source).
Further, in this kind of control equipment,
1. Various check functions for preventing malfunction are included corresponding to the controlled systems but, in many cases, these check functions are not assured in the case of an abnormality in the power source system;
2. It is desired that stored contents of various memory circuits be retained at the time of the power source being ON and OFF; and
3. It is desired that no unnecessary signals be sent from the interface circuit to a controlled system, for instance, a machine tool in a transient state at the time of the ON-OFF operation of the power source.
For the abovesaid reasons, the control equipment power source arrangement is required to have the following functions:
(1) A function of detecting power source abnormalities and cutting off the power source for preventing malfunctions resulting therefrom;
(2) maintenance of a power down sequence for preventing malfunctions at the time of the ON-OFF operation of the power source; and
(3) a function of quickly providing power source OFF information to the control equipment to stop, for example, the read/write operation of the memory circuit.
To achieve such functions as mentioned above, according to the prior art, for example, as shown in FIG. 1, a control equipment power source 102 having a control circuit power source 100 and a driving power source 101 is provided with a control circuit power source abnormality detecting circuit (hereinafter referred to as the EC power source abnormality detecting circuit) 103 for detecting abnormalities in the control circuit power source 100 and a driving power source abnormality detecting circuit (hereinafter referred to as the ED power source abnormality detecting circuit) 104 for detecting abnormalities in the driving power source 101, and outputs from the both detecting circuits are processed to perform a power down sequence such, for instance, as shown in FIG. 2, thereby performing the above-mentioned functions (1) and (3).
That is, when a power source switch 105 is turned ON to connect an AC power source 106 to the control equipment power source 102, an output Ec from the control circuit equipment power source 100 is caused to rise first and then, at the moment when the output Ec reaches its steady state, an output Ed from the driving power source 101 is caused to rise. At the moment when the outputs Ec and Ed both reach the steady state, an enable signal EN, which informs control equipment 107 of the presence or absence of a power source abnormality, is turned ON, thereby preventing malfunction of the control equipment 107 and a controlled system 108. When a power source abnormality is detected by the detecting circuits 103 and 104, the enable signal EN is immediately turned OFF and, after a predetermined period of time, the driving power source 101 is forcibly turned OFF and the power source switch 105 is turned OFF by a switch control signal or an alarm signal ALM, by which the driving power source output Ed is completely turned OFF before the output Ec from the control circuit power source 100 becomes unstable as shown in FIG. 2, thus preventing malfunction. Further, since the enable signal EN is turned OFF first, the operation of the memory circuit can be stopped quickly when the power source is turned OFF.
In such control equipment as mentioned above, it happens that when the control function is extended, for instance, when the number of axes to be controlled is increased in numerical control equipment, the power source capacity becomes insufficient only with the control equipment power source 102 shown in FIG. 1 and one more power source must be provided. For example, there are some occasions when the addition of an extension 300 to the control equipment 107 is accompanied by the provision of a driving power source 301 alone as shown in FIG. 3, a control circuit power source 400 alone as shown in FIG. 4 or a control circuit power source 500 and a driving power source 501 as shown in FIG. 5. In FIGS. 3 to 5, the parts corresponding to those in FIG. 1 are identified by the same reference numerals, and 302 indicates increased power sources.
In such a compound power source in which an additional power source is provided separately from a main power source, it is necessary that the aforementioned functions be satisfied as a whole. The prior art merely adopts an arrangement such that only the main power source performs such a power down sequence as shown in FIG. 2, or the main power source and the additional power source execute the above-described power down sequence independently of each other. Accordingly, the prior art has defects that, for example, even if the additional power source is broken down, the main power source continues to operate, that the sequence shown in FIG. 2 is not satisfied between the output Ec.sub.1 from the control circuit power source of the main power soruce and the output Ed.sub.2 from the driving power source of the additional power source, and that since the compound power source, as viewed from the side of the control equpment, cannot be regarded as one power source connected thereto, processing in the case of a power source abnormality is complex and difficult on the side of the control equipment.